Method for preparing active magnesium oxide from laterite nickel ore nickel precipitation wastewater

Abstract

The application provides a method for preparing active magnesium oxide from laterite nickel ore nickel precipitation wastewater, and relates to the technical field of magnesium oxide preparation. The method comprises the following steps: S1, collecting laterite nickel ore nickel precipitation wastewater, S2, multi-stage cooperative impurity removal, S3, ultrasonic dispersant composite carbonization, S4, microwave-assisted hydrothermal activation, S5, structured anti-fouling calcination, S6, surface modification and functional modification, S7, mother liquor circulation and resource utilization, and S8, active magnesium oxide. Through multi-stage cooperative impurity removal and gradient calcination, the magnesium recovery rate is improved compared with the traditional process, 6-12 kg of high-purity magnesium sulfate can be extracted per ton of wastewater, the raw material dependence of laterite nickel ore smelting is significantly reduced, the concentrated mother liquor is purified and recycled for more than 8 times, water consumption is reduced, and comprehensive energy consumption is reduced. The active magnesium oxide obtained by the method has a purity of 98.5% or more, a uniform particle size distribution, and a specific surface area of 85-120 m 2 / g, and exhibits excellent surface activity and reaction activity.

Description

Technical Field

[0001] This invention relates to the field of magnesium oxide preparation technology, specifically a method for preparing active magnesium oxide from nickel precipitate wastewater from laterite nickel ore. Background Technology

[0002] Laterite nickel ore precipitation wastewater is a typical industrial wastewater generated in the hydrometallurgical process of laterite nickel ore. It mainly originates from the sulfide precipitation process. During the acid leaching of laterite nickel ore, valuable metals such as nickel and cobalt enter the liquid phase in the form of sulfates. Subsequently, nickel and cobalt are selectively recovered through neutralization and precipitation. The remaining waste liquid is the precipitation wastewater, which contains a large amount of magnesium ions and trace amounts of heavy metal ions. The high concentration of magnesium ions in the precipitation wastewater of laterite nickel ore leads to the waste of magnesium resources if discharged directly. By preparing activated magnesium oxide, a magnesium recovery rate of over 95% can be achieved, and 6-12 kg of magnesium sulfate can be extracted from each ton of wastewater, significantly reducing the dependence on raw materials.

[0003] Existing methods for preparing active magnesium oxide from laterite nickel ore precipitated wastewater still have some problems. The lime neutralization method has a magnesium recovery rate of less than 30% and generates a large amount of gypsum slag, producing 2.5-3 tons of waste slag per ton of wastewater, causing secondary pollution and high treatment costs. Although the traditional calcination method can produce magnesium oxide, it has high energy consumption, sodium salt accumulation leads to soil salinization, and excessive sulfate ions cause water acidification. Therefore, those skilled in the art provide a method for preparing active magnesium oxide from laterite nickel ore precipitated wastewater to solve the problems mentioned in the background art. Summary of the Invention

[0004] Technical problems to be solved To address the shortcomings of existing technologies, this invention provides a method for preparing active magnesium oxide from nickel ore precipitation wastewater in laterite nickel mines. This method solves the problems of magnesium recovery rate <30% and the generation of a large amount of gypsum slag in lime neutralization method, which generates 2.5-3 tons of waste slag per ton of wastewater, causing secondary pollution and high treatment costs. While the traditional calcination method can produce magnesium oxide, it has high energy consumption, sodium salt accumulation leading to soil salinization, and excessive sulfate causing water acidification.

[0005] Technical solution To achieve the above objectives, the present invention provides the following technical solution: a method for preparing active magnesium oxide from laterite nickel ore precipitate wastewater, comprising the following steps: S1. Collection of nickel precipitation wastewater from laterite nickel ore: The collected wastewater is initially filtered through a filter screen to remove suspended solids and impurities, resulting in pretreated wastewater. The pretreated wastewater is then introduced into a filtration tank. S2. Multi-stage synergistic impurity removal, targeting the removal of heavy metal Ni. 2+ Co 2+ with Fe 3+ To obtain a high-purity magnesium salt solution by removing suspended solids; S3. Ultrasonic dispersant composite carbonization to prepare a high specific surface area basic magnesium carbonate precursor: Under ultrasonic assistance, CO2 is passed into a magnesium salt solution to carry out the carbonization reaction. The reaction temperature is controlled at 40-50℃, and the ultrasonic power is 200-300 W to promote uniform mixing of the gas-liquid-solid three phases, significantly improving carbonization efficiency and particle dispersibility. The final pH of the reaction is 6.5-7.0, and the generated basic magnesium carbonate precipitate is separated by centrifugation and washed with deionized water until no SO4 is present. 2- Vacuum drying at 60-80℃ for 12 h yielded a precursor with a specific surface area of ​​180-220 m². 2 / g, with a concentrated particle size distribution, laying the foundation for subsequent calcination to prepare highly active magnesium oxide; S4. Microwave-assisted hydrothermal activation promotes the lattice reconstruction of basic magnesium carbonate precursor through the synergistic effect of microwave irradiation and hydrothermal environment, significantly improving its thermal decomposition kinetic rate and reducing calcination activation energy. S5. Structured anti-scalding calcination, gradient temperature calcination, to achieve crystal phase stability and pore structure optimization. A programmable temperature-controlled muffle furnace is used to raise the temperature from room temperature to 450℃ at a rate of 2-3℃ / min, hold for 2 h, and then raise the temperature to 650℃ at a rate of 1-2℃ / min, and hold for another 3 h to fully stabilize the active magnesium oxide crystal phase and optimize the pore structure. S6. Surface modification and functionalization: An organosilane coupling agent ethanol solution was introduced into the active magnesium oxide powder obtained by gradient heating calcination. The mixture was reacted at 80°C for 2 h under stirring conditions, so that the silane molecules underwent hydrolysis and condensation on the magnesium oxide surface to form a dense organic-inorganic hybrid coating layer, which effectively reduced the surface energy and inhibited the aggregation of nanoparticles. S7. Mother liquor recycling and resource utilization: evaporation and crystallization, triple-effect evaporation to recover Na2SO4·10H2O and CaSO4·2H2O, achieving efficient separation and resource utilization of sodium and calcium salts. The mother liquor is recycled back to the precursor preparation process after purification. The number of cycles can reach more than 8 times, improving the salt recovery rate, significantly reducing wastewater discharge and raw material consumption, reducing system water consumption, and reducing overall energy consumption year-on-year. Secondary steam is used as a heat source for the carbonization process, which is more energy-efficient. Condensate is recycled, and the water used for cleaning filter residue in the pretreatment process is recycled for system replenishment after multi-stage filtration and pH adjustment. S8. Activated magnesium oxide, the modified product is selected for use in polypropylene composite systems. Flame-retardant composite materials are prepared by melt blending, with improved LOI value, achieving V-0 rating in vertical burning, and high mechanical property retention.

[0006] Preferably, step S2 above further includes: S2.1. Primary impurity removal, sulfide precipitation-complexation synergistic process, process parameters: add Na2S at a ratio of 1.1-1.2 times, pH 5-6, and simultaneously add EDTA at a ratio of 0.05-0.1 g / L to form Ni-EDTA and Co-EDTA complexes; S2.2. Secondary impurity removal, calcium, aluminum and silicon synergistic removal, process parameters: add lime slurry at a ratio of 1.05-1.1 times, pH 8-9, add diatomaceous earth at a ratio of 0.5-1.0 g / L as a filter aid; S2.3. Three-stage impurity removal, deep purification through oxidation and adsorption; process parameters: ozone is introduced at a concentration of 0.8-1.0 g / L to oxidize residual Fe. 2+ For Fe 3+ Simultaneously add bentonite with a modified content of 1.2-1.5 g / L to adsorb precipitates, thereby achieving efficient removal of suspended solids and colloids; After three-stage synergistic treatment, Ni in the magnesium salt solution 2+ Co 2+ Fe 3+ The concentrations are all below 0.1 mg / L, and the turbidity is less than 1 NTU, which meets the requirements for raw materials for the preparation of active magnesium oxide. The sulfide precipitant is a compound system of Na2S and sulfur, with the sulfur content being 10 to 20 wt.%.

[0007] Preferably, the furnace lining of the rotary gradient calcining furnace in step S5 is a silicon carbide-zirconia composite ceramic. Dynamic atmosphere control is employed. During the initial calcination stage (0-30 minutes), nitrogen gas at a flow rate of 0.5-0.8 L / min is introduced to maintain an oxygen volume fraction of 8%-10%. During the subsequent 30-90 minutes, a nitrogen-air mixture is introduced, with an oxygen volume fraction of 10%-12%, to suppress over-sintering and promote directional grain growth. This ensures that the active magnesium oxide maintains a high specific surface area and reactivity at high temperatures. This calcination process, combined with atmosphere control, effectively avoids excessive crystallization and surface densification of the active magnesium oxide, ensuring the density of reaction sites in subsequent functionalization modifications. Simultaneously, it improves the dispersion and interfacial compatibility of the final product in the polymer matrix, further enhancing the flame retardant properties and mechanical stability of the composite material. By controlling the oxygen partial pressure, abnormal grain growth is suppressed, resulting in a porous and loose structure in the calcined product, with a stable specific surface area of ​​85-120 m². 2 / g, significantly improving surface hydroxyl density and chemical activity.

[0008] Preferably, in step S4 above, the reaction is carried out for 60-90 min under microwave power of 800-1000 W and hydrothermal temperature of 160-180℃, during which the precursor completes the ordered crystalline phase transformation, generating active magnesium oxide with uniform particle size and well-developed pores. XRD characterization of the product shows a purity higher than 98% and a BET specific surface area of ​​240-280 m².2 / g, with an average pore size distribution between 3-5 nm, exhibiting excellent surface activity and adsorption properties.

[0009] Preferably, step S5 above further includes: S5.1 The cooling stage uses an inert atmosphere to prevent the product from absorbing moisture and agglomerating; S5.2. The final magnesium oxide powder is loose and porous, with a BET specific surface area maintained between 230 and 260 m². 2 / g, with a pore volume of 0.8 to 1.0 cm³. 3 / g, with uniform crystal size and no obvious sintering phenomenon, effectively ensuring its high activity performance in catalysis, adsorption and environmental remediation.

[0010] Preferably, the active magnesium oxide, after being functionalized with a silane coupling agent, achieves nanoscale uniform dispersion in the polypropylene matrix, enhancing interfacial bonding and effectively promoting char layer densification. This improves the thermal stability and flame retardant synergy of the composite material while preventing mechanical property degradation, meeting the application requirements of high-end flame retardant materials. The calcined product, after instantaneous cooling, fixes lattice defects and rapidly locks high-energy active sites, further enhancing surface reactivity. During the functionalization process, the silanol groups generated by the hydrolysis of the silane coupling agent condense with the hydroxyl groups on the surface of the active magnesium oxide to form stable Si-O-Mg bonds, significantly enhancing the interfacial bonding between the inorganic phase and the organic matrix. This composite material exhibits increased char residue at 800℃, a high limiting oxygen index, and improved tensile strength retention, meeting the UL94 V-0 flame retardant standard while also possessing excellent mechanical properties.

[0011] Preferably, step S6 above further includes: S6.1. The modified product exhibits significantly improved dispersion stability in nonpolar solvents, with the contact angle increasing from 35° to 105°, demonstrating excellent hydrophobic properties; S6.2. At the same time, it retains a high specific surface area, the pore structure is not damaged, the surface functional groups are abundant, and the interfacial bonding ability with the polymer matrix is ​​enhanced.

[0012] Preferably, step S8 further includes: S8.1. Pb in simulated wastewater treatment 2+ The adsorption capacity reaches 135 mg / g, and it still retains more than 92% of its initial activity after five cycles of use; S8.2. Further verification of its long-term stability: Functionalized magnesium oxide was used in actual industrial wastewater treatment. After 30 days of continuous operation, the adsorption performance showed no significant decline, the removal rate of heavy metal ions remained stable at over 95%, and the effluent quality met the national discharge standards. S8.3. Simultaneously, the material is easily regenerated, and after 10 cycles of pickling and heat treatment, its structural integrity remains good, with the specific surface area maintained at 200 m². 2 With a yield of / g or more, it possesses the feasibility and economic advantages for large-scale industrial application.

[0013] Beneficial effects This invention provides a method for preparing activated magnesium oxide from nickel precipitate wastewater from laterite nickel ore. It has the following beneficial effects: In this invention, through multi-stage synergistic impurity removal and gradient calcination, the magnesium recovery rate is improved compared with the traditional process. 6-12 kg of high-purity magnesium sulfate can be extracted from each ton of wastewater, which significantly reduces the raw material dependence of laterite nickel ore smelting. The concentrated mother liquor can be recycled more than 8 times after purification, reducing water consumption and overall energy consumption.

[0014] In this invention, a dual-frequency microwave field of 2.45 GHz + 915 GHz is used to improve the uniformity of precursor grains and achieve a specific surface area of ​​240-280 m². 2 / g, which is 3 times higher than the traditional calcination method, reduces energy consumption from 2.1 t steam / ton of product to 0.35 t steam / ton of product, reduces carbon emissions, and introduces nitrogen gas in the early stage of calcination to inhibit excessive sintering of magnesium oxide, and switches to nitrogen-air mixture in the later stage to maintain porosity and stabilize specific surface area.

[0015] In this invention, the specific surface area of ​​active magnesium oxide reaches 240-280 m². 2 / g, pore volume 0.8-1.0 cm³ 3 / g, for Pb 2+ With an adsorption capacity of 135 mg / g and an activity retention of 92% after 5 cycles, it is suitable for industrial wastewater treatment. The modified magnesium oxide is used in polypropylene composites, increasing the LOI value to 32% and achieving V-0 rating for vertical combustion. At the same time, the tensile strength retention rate is >85%, overcoming the negative impact of traditional flame retardants on mechanical properties. Attached Figure Description

[0016] Figure 1 This is a schematic diagram of the process of the present invention. Detailed Implementation

[0017] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0018] Example 1: like Figure 1As shown in the figure, this invention provides a method for preparing active magnesium oxide from nickel precipitate wastewater from laterite nickel ore, comprising the following steps: S1. Collection of nickel precipitation wastewater from laterite nickel ore: The collected wastewater is initially filtered through a filter screen to remove suspended solids and impurities, resulting in pretreated wastewater. The pretreated wastewater is then introduced into a filtration tank. S2. Multi-stage synergistic impurity removal, targeting the removal of heavy metal Ni. 2+ Co 2+ with Fe 3+ To obtain a high-purity magnesium salt solution by removing suspended solids; S2.1. Primary impurity removal, sulfide precipitation-complexation synergy: The process utilizes the synergistic effect of Na2S and EDTA to construct a "selective chelation-precipitation" microenvironment. Through the dual action of sulfide precipitation kinetics and complexation enhancement mechanisms, efficient removal of heavy metals is achieved. In a weakly acidic environment with pH 5.0-6.0, Na2S reacts with Ni... 2+ Theoretically required sulfur is added at a ratio of 1.1-1.2 times, with a stoichiometric ratio of 1:1. This allows nickel and cobalt ions to react rapidly with sulfur ions to form NiS and CoS nanoprecipitates, thus inhibiting sulfur production. 2- Hydrolysis generates H2S gas and enhances complexation stability. EDTA is added simultaneously as an auxiliary complexing agent, which binds to unprecipitated Ni through multidentate coordination. 2+ Co 2+ The system forms stable chelates and simultaneously alters the surface charge distribution of minerals to promote the aggregation of fine particles. By optimizing the Na2S dosage using response surface methodology and combining it with an online pH control system, the system achieves a heavy metal removal rate of >98% without secondary pollution. A segmented dosing system is used to achieve gradient dosing of Na2S and EDTA, and a tubular microfiltration membrane is used to complete the rapid separation of sludge and water, thereby improving the efficiency of solid-liquid separation. S2.2. Secondary impurity removal, synergistic removal of calcium, aluminum, and silicon, constructing a three-in-one purification unit of "alkaline precipitation - carrier loading - filter aid enhancement". Deep removal of iron and aluminum impurities is achieved through the synergistic effect of lime slurry and diatomaceous earth. Under alkaline conditions of pH 8.5-9.0, Ca... 2+ with Fe 3+ Al 3+ Fe(OH)3 and Al(OH)3 precipitates were generated respectively. After modification with phosphoric acid, the specific surface area of ​​diatomaceous earth increased from 25 m². 2 / g increased to 250 m 2 / g, forming a rigid framework structure to coat heavy metal hydroxides, the modified diatomaceous earth enhances the stability of the interlayer domain through the chemical bonding of phosphate groups, and at the same time introduces negatively charged active sites to improve adsorption performance. Optimization of process parameters shows that when the lime slurry ratio is 1.05-1.1 times and the diatomaceous earth dosage is 0.5-1.0 g / L, the iron removal rate is >98% and the filter cake moisture content is <60%. Combined with an ABS material sequencing batch adsorption tower, it achieves efficient solid-liquid separation and improves the corrosion resistance of the equipment. S2.3. Three-stage impurity removal, deep purification through oxidation and adsorption, integrating a multi-level barrier of "advanced oxidation - selective adsorption - flocculation and sedimentation". Through the synergistic effect of ozone oxidation and modified bentonite, it achieves ultimate purification of colloidal heavy metals. In a weakly alkaline environment of pH 8-9, ozone removes residual Fe through a free radical chain reaction. 2+ Oxidized to Fe 3+ Simultaneously, it disrupts colloidal stability. Modified bentonite, after dual modification with NaCl and CTAB, increases its interlayer spacing from 1.2 nm to 2.8 nm, forming positively charged active sites on its surface. Through multiple processes of electrostatic adsorption, ion exchange, and surface complexation, it captures hydrophobic heavy metals. With an ozone dosage of 0.8-1.0 g / L and a contact time of 45-60 min, Fe... 3+ The removal rate is improved, and the bentonite adsorption capacity reaches 12.5 mg / g. The ozone microbubble generator and sequencing batch adsorption tower are linked together, and the intelligent control system is combined to reduce the consumption of reagents. After three-stage synergistic treatment, Ni in the magnesium salt solution 2+ Co 2+ Fe 3+ The concentrations are all below 0.1 mg / L, and the turbidity is less than 1 NTU, meeting the requirements for raw materials in the preparation of active magnesium oxide. The sulfide precipitant is a compound system of Na2S and sulfur, with sulfur accounting for 10 to 20 wt.%. This compound system generates polysulfides in situ under acidic conditions, which can effectively enhance the precipitation of Cu. 2+ Zn 2+ The selective precipitation of heavy metal ions avoids the burden of subsequent desulfurization caused by the introduction of excessive sulfides, while polysulfides have a stronger reducing ability in acidic media.

[0019] S3. Ultrasonic dispersant composite carbonization to prepare a high specific surface area basic magnesium carbonate precursor: Under ultrasonic assistance, CO2 is passed into a magnesium salt solution to carry out the carbonization reaction. The reaction temperature is controlled at 40-50℃, and the ultrasonic power is 200-300 W to promote uniform mixing of the gas-liquid-solid three phases, significantly improving carbonization efficiency and particle dispersibility. The final pH of the reaction is 6.5-7.0, and the generated basic magnesium carbonate precipitate is separated by centrifugation and washed with deionized water until no SO4 is present. 2- Vacuum drying at 60-80℃ for 12 h yielded a precursor with a specific surface area of ​​180-220 m².2 / g, with a concentrated particle size distribution, lays the foundation for the subsequent calcination preparation of highly active magnesium oxide. The cavitation effect of ultrasound effectively inhibits particle agglomeration and further optimizes the microstructure of the precursor.

[0020] S4. Microwave-assisted hydrothermal activation: Through the synergistic effect of microwave irradiation and hydrothermal environment, the lattice reconstruction of basic magnesium carbonate precursor is promoted, significantly improving its thermal decomposition kinetic rate and reducing the calcination activation energy. The microwave power is set to 600-800 W, the hydrothermal temperature is controlled at 120-150℃, and the reaction time is 2-3 h, so that the precursor is fully activated and the grains are refined. S5. Structured anti-scalding calcination, gradient temperature calcination, to achieve crystal phase stability and pore structure optimization. A programmable temperature-controlled muffle furnace is used to raise the temperature from room temperature to 450℃ at a rate of 2-3℃ / min, hold for 2 h, and then raise the temperature to 650℃ at a rate of 1-2℃ / min, and hold for another 3 h to fully stabilize the active magnesium oxide crystal phase and optimize the pore structure. S5.1 The cooling stage uses an inert atmosphere to prevent the product from absorbing moisture and agglomerating; S5.2. The final magnesium oxide powder is loose and porous, with a BET specific surface area maintained between 230 and 260 m². 2 / g, with a pore volume of 0.8 to 1.0 cm³. 3 With uniform crystal size and no obvious sintering, this material effectively ensures high activity in catalysis, adsorption, and environmental remediation. In simulated industrial waste gas treatment, it exhibits excellent CO2 adsorption capacity, reaching 1.8 mmol / g at 25℃. After five cycles, the activity retention rate exceeds 92%, demonstrating potential for large-scale application. This magnesium oxide material can also be used for heavy metal ion adsorption, particularly for Pb. 2+ Cd 2+ The adsorption capacities reached 2.1 mmol / g and 1.9 mmol / g, respectively, with an adsorption equilibrium time of less than 30 min, demonstrating rapid and efficient removal capabilities. Its porous structure and high surface active site density effectively promoted ion diffusion and coordination. After five adsorption-desorption cycles, the structural integrity remained good, with performance degradation of less than 8% and high regeneration rate. This material has advantages such as low preparation cost and strong process controllability, making it suitable for deep purification of industrial wastewater and resource recovery scenarios, with broad application prospects.

[0021] S6. Surface modification and functionalization: An organosilane coupling agent ethanol solution was introduced into the active magnesium oxide powder obtained by gradient heating calcination. The mixture was reacted at 80°C for 2 h under stirring conditions, so that the silane molecules underwent hydrolysis and condensation on the magnesium oxide surface to form a dense organic-inorganic hybrid coating layer, which effectively reduced the surface energy and inhibited the aggregation of nanoparticles. S6.1. The modified product exhibits significantly improved dispersion stability in nonpolar solvents, with the contact angle increasing from 35° to 105°, demonstrating excellent hydrophobic properties; S6.2. It also retains a high specific surface area, with an intact pore structure and abundant surface functional groups, enhancing its interfacial bonding with the polymer matrix and further improving the interfacial compatibility and stress transfer efficiency of the composite material. S7. Mother liquor recycling and resource utilization: evaporation and crystallization, triple-effect evaporation to recover Na2SO4·10H2O and CaSO4·2H2O, achieving efficient separation and resource utilization of sodium and calcium salts. The mother liquor is recycled back to the precursor preparation process after purification. The number of cycles can reach more than 8 times, improving the salt recovery rate, significantly reducing wastewater discharge and raw material consumption, reducing system water consumption, and reducing overall energy consumption year-on-year. Secondary steam is used as a heat source for the carbonization process, which is more energy-efficient. Condensate is recycled, and the water used to clean the filter residue in the pretreatment process is recycled for system replenishment after multi-stage filtration and pH adjustment. The entire process achieves zero discharge of waste residue and cascade utilization of water resources, realizing green and low-carbon production.

[0022] S8. Activated magnesium oxide, the modified product is selected for use in polypropylene composite system, and flame-retardant composite material is prepared by melt blending method. The LOI value is improved, the vertical burning reaches V-0 level, and the mechanical properties are well retained. S8.1. Pb in simulated wastewater treatment 2+ The adsorption capacity reaches 135 mg / g, and it still retains more than 92% of its initial activity after five cycles of use; S8.2. Further verification of its long-term stability: Functionalized magnesium oxide was used in actual industrial wastewater treatment. After 30 days of continuous operation, the adsorption performance showed no significant decline, the removal rate of heavy metal ions remained stable at over 95%, and the effluent quality met the national discharge standards. S8.3. Simultaneously, the material is easily regenerated, and after 10 cycles of pickling and heat treatment, its structural integrity remains good, with the specific surface area maintained at 200 m². 2 With a yield of over / g, this material possesses feasibility and economic advantages for large-scale industrial application. In practical engineering applications, it exhibits excellent processability and environmental adaptability, superior acid and alkali resistance, and structural stability during long-term service, with no significant dissolution or deactivation.

[0023] The rotary gradient calcining furnace described in step S5 above has a silicon carbide-zirconia composite ceramic lining. Dynamic atmosphere control is employed. During the initial calcination stage (0-30 minutes), nitrogen gas at a flow rate of 0.5-0.8 L / min is introduced to maintain an oxygen volume fraction of 8%-10%. During the subsequent 30-90 minutes, a nitrogen-air mixture is introduced, with an oxygen volume fraction of 10%-12%, to suppress over-sintering and promote directional grain growth. This ensures that the active magnesium oxide maintains a high specific surface area and reactivity at high temperatures. This calcination process, combined with atmosphere control, effectively avoids excessive crystallization and surface densification of the active magnesium oxide, ensuring the density of reaction sites in subsequent functionalization modifications. Simultaneously, it improves the dispersion and interfacial compatibility of the final product in the polymer matrix, further enhancing the flame retardant properties and mechanical stability of the composite material. By controlling the oxygen partial pressure, abnormal grain growth is suppressed, resulting in a porous and loose structure in the calcined product with a stable specific surface area of ​​85-120 m². 2 / g, significantly improving surface hydroxyl density and chemical activity.

[0024] In step S4 above, the reaction is carried out for 60-90 minutes under microwave power of 800-1000 W and hydrothermal temperature of 160-180℃. The precursor completes the ordered crystalline phase transformation, generating active magnesium oxide with uniform particle size and well-developed pores. XRD characterization of the product shows a purity higher than 98% and a BET specific surface area of ​​240-280 m². 2 / g, with an average pore size distribution between 3-5 nm, exhibiting excellent surface activity and adsorption properties.

[0025] The active magnesium oxide, after being functionalized with a silane coupling agent, achieves nanoscale uniform dispersion in a polypropylene matrix, enhancing interfacial bonding and effectively promoting char layer densification. This improves the thermal stability and flame retardant synergy of the composite material while preventing mechanical property degradation, meeting the application requirements of high-end flame retardant materials. The calcined product is instantly cooled to fix lattice defects and rapidly lock high-energy active sites, further enhancing surface reactivity. During the functionalization process, the silanol groups generated by the hydrolysis of the silane coupling agent condense with the hydroxyl groups on the surface of the active magnesium oxide to form stable Si-O-Mg bonds, significantly enhancing the interfacial bonding between the inorganic phase and the organic matrix. This composite material exhibits improved char residue at 800℃, a high limiting oxygen index, and improved tensile strength retention, meeting the UL94 V-0 flame retardant standard while also possessing excellent mechanical properties.

[0026] Although embodiments of the invention have been shown and described, it will be understood by those skilled in the art that various changes, modifications, substitutions and alterations can be made to these embodiments without departing from the principles and spirit of the invention, the scope of which is defined by the appended claims and their equivalents.

Claims

1. A method for preparing activated magnesium oxide from nickel precipitate wastewater from laterite nickel ore, characterized in that: Includes the following steps: S1. Collection of nickel precipitation wastewater from laterite nickel ore: The collected wastewater is initially filtered through a filter screen to remove suspended solids and impurities, resulting in pretreated wastewater. The pretreated wastewater is then introduced into a filtration tank. S2. Multi-stage synergistic impurity removal, targeting the removal of heavy metal Ni. 2+ Co 2+ with Fe 3+ To obtain a high-purity magnesium salt solution by removing suspended solids; S3. Ultrasonic dispersant composite carbonization to prepare a high specific surface area basic magnesium carbonate precursor: Under ultrasonic assistance, CO2 is passed into a magnesium salt solution to carry out the carbonization reaction. The reaction temperature is controlled at 40-50℃, and the ultrasonic power is 200-300 W to promote uniform mixing of the gas-liquid-solid three phases, significantly improving carbonization efficiency and particle dispersibility. The final pH of the reaction is 6.5-7.0, and the generated basic magnesium carbonate precipitate is separated by centrifugation and washed with deionized water until no SO4 is present. 2- Vacuum drying at 60-80℃ for 12 h yielded a precursor with a specific surface area of ​​180-220 m². 2 / g, with a concentrated particle size distribution, laying the foundation for subsequent calcination to prepare highly active magnesium oxide; S4. Microwave-assisted hydrothermal activation promotes the lattice reconstruction of basic magnesium carbonate precursor through the synergistic effect of microwave irradiation and hydrothermal environment, significantly improving its thermal decomposition kinetic rate and reducing calcination activation energy. S5. Structured anti-scalding calcination, gradient temperature calcination, to achieve crystal phase stability and pore structure optimization. A programmable temperature-controlled muffle furnace is used to raise the temperature from room temperature to 450℃ at a rate of 2-3℃ / min, hold for 2 h, and then raise the temperature to 650℃ at a rate of 1-2℃ / min, and hold for another 3 h to fully stabilize the active magnesium oxide crystal phase and optimize the pore structure. S6. Surface modification and functionalization: An organosilane coupling agent ethanol solution was introduced into the active magnesium oxide powder obtained by gradient heating calcination. The mixture was reacted at 80°C for 2 h under stirring conditions, so that the silane molecules underwent hydrolysis and condensation on the magnesium oxide surface to form a dense organic-inorganic hybrid coating layer, which effectively reduced the surface energy and inhibited the aggregation of nanoparticles. S7. Mother liquor recycling and resource utilization: evaporation and crystallization, triple-effect evaporation to recover Na2SO4·10H2O and CaSO4·2H2O, achieving efficient separation and resource utilization of sodium and calcium salts. The mother liquor is recycled back to the precursor preparation process after purification. The number of cycles can reach more than 8 times, improving the salt recovery rate, significantly reducing wastewater discharge and raw material consumption, reducing system water consumption, and reducing overall energy consumption year-on-year. Secondary steam is used as a heat source for the carbonization process, which is more energy-efficient. Condensate is recycled, and the water used for cleaning filter residue in the pretreatment process is recycled for system replenishment after multi-stage filtration and pH adjustment. S8. Activated magnesium oxide, the modified product is selected for use in polypropylene composite systems. Flame-retardant composite materials are prepared by melt blending, with improved LOI value, achieving V-0 rating in vertical burning, and high mechanical property retention.

2. The method for preparing active magnesium oxide from nickel precipitate wastewater from laterite nickel ore according to claim 1, characterized in that: Step S2 above also includes: S2.

1. Primary impurity removal, sulfide precipitation-complexation synergistic process, process parameters: add Na2S at a ratio of 1.1-1.2 times, pH 5-6, and simultaneously add EDTA at a ratio of 0.05-0.1 g / L to form Ni-EDTA and Co-EDTA complexes; S2.

2. Secondary impurity removal, calcium, aluminum and silicon synergistic removal, process parameters: add lime slurry at a ratio of 1.05-1.1 times, pH 8-9, add diatomaceous earth at a ratio of 0.5-1.0 g / L as a filter aid; S2.

3. Three-stage impurity removal, deep purification through oxidation and adsorption; process parameters: ozone is introduced at a concentration of 0.8-1.0 g / L to oxidize residual Fe. 2+ For Fe 3+ Simultaneously add bentonite with a modified content of 1.2-1.5 g / L to adsorb precipitates, thereby achieving efficient removal of suspended solids and colloids; After three-stage synergistic treatment, Ni in the magnesium salt solution 2+ Co 2+ Fe 3+ The concentrations are all below 0.1 mg / L, and the turbidity is less than 1 NTU, which meets the requirements for raw materials for the preparation of active magnesium oxide. The sulfide precipitant is a compound system of Na2S and sulfur, with the sulfur content being 10 to 20 wt.%.

3. The method for preparing active magnesium oxide from nickel precipitate wastewater from laterite nickel ore according to claim 1, characterized in that: The rotary gradient calcining furnace described in step S5 above has a silicon carbide-zirconia composite ceramic lining. Dynamic atmosphere control is employed. During the initial calcination stage (0-30 minutes), nitrogen gas at a flow rate of 0.5-0.8 L / min is introduced to maintain an oxygen volume fraction of 8%-10%. During the subsequent 30-90 minutes, a nitrogen-air mixture is introduced, with an oxygen volume fraction of 10%-12%, to suppress over-sintering and promote directional grain growth. This ensures that the active magnesium oxide maintains a high specific surface area and reactivity at high temperatures. This calcination process, combined with atmosphere control, effectively avoids excessive crystallization and surface densification of the active magnesium oxide, ensuring the density of reaction sites in subsequent functionalization modifications. Simultaneously, it improves the dispersion and interfacial compatibility of the final product in the polymer matrix, further enhancing the flame retardant properties and mechanical stability of the composite material. By controlling the oxygen partial pressure, abnormal grain growth is suppressed, resulting in a porous and loose structure in the calcined product with a stable specific surface area of ​​85-120 m². 2 / g, significantly improving surface hydroxyl density and chemical activity.

4. The method for preparing active magnesium oxide from nickel precipitate wastewater from laterite nickel ore according to claim 1, characterized in that: In step S4 above, the reaction is carried out for 60-90 min under microwave power of 800-1000 W and hydrothermal temperature of 160-180℃. The precursor completes the ordered crystalline phase transformation, generating active magnesium oxide with uniform particle size and well-developed pores. XRD characterization of the product shows a purity higher than 98% and a BET specific surface area of ​​240-280 m². 2 / g, with an average pore size distribution between 3-5 nm, exhibiting excellent surface activity and adsorption properties.

5. The method for preparing active magnesium oxide from nickel precipitate wastewater from laterite nickel ore according to claim 1, characterized in that: Step S5 above also includes: S5.1 The cooling stage uses an inert atmosphere to prevent the product from absorbing moisture and agglomerating; S5.

2. The final magnesium oxide powder is loose and porous, with a BET specific surface area maintained between 230 and 260 m². 2 / g, with a pore volume of 0.8 to 1.0 cm³. 3 / g, with uniform crystal size and no obvious sintering phenomenon, effectively ensuring its high activity performance in catalysis, adsorption and environmental remediation.

6. The method for preparing active magnesium oxide from nickel precipitate wastewater from laterite nickel ore according to claim 3, characterized in that: The active magnesium oxide, after being functionalized with a silane coupling agent, achieves nanoscale uniform dispersion in a polypropylene matrix, enhancing interfacial bonding and effectively promoting char layer densification. This improves the thermal stability and flame retardant synergy of the composite material while preventing mechanical property degradation, meeting the application requirements of high-end flame retardant materials. The calcined product, after instantaneous cooling, fixes lattice defects and rapidly locks high-energy active sites, further enhancing surface reactivity. During the functionalization process, the silanol groups generated by the hydrolysis of the silane coupling agent condense with the hydroxyl groups on the surface of the active magnesium oxide to form stable Si-O-Mg bonds, significantly enhancing the interfacial bonding between the inorganic phase and the organic matrix. This composite material exhibits improved char residue at 800℃, a high limiting oxygen index, and improved tensile strength retention, meeting the UL94V-0 flame retardant standard while also possessing excellent mechanical properties.

7. The method for preparing active magnesium oxide from nickel precipitate wastewater from laterite nickel ore according to claim 1, characterized in that: Step S6 above also includes: S6.

1. The modified product exhibits significantly improved dispersion stability in nonpolar solvents, with the contact angle increasing from 35° to 105°, demonstrating excellent hydrophobic properties; S6.

2. At the same time, it retains a high specific surface area, the pore structure is not damaged, the surface functional groups are abundant, and the interfacial bonding ability with the polymer matrix is ​​enhanced.

8. The method for preparing active magnesium oxide from nickel precipitate wastewater from laterite nickel ore according to claim 1, characterized in that: The above step S8 also includes: S8.

1. Pb in simulated wastewater treatment 2+ The adsorption capacity reaches 135 mg / g, and it still retains more than 92% of its initial activity after five cycles of use; S8.

2. Further verification of its long-term stability: Functionalized magnesium oxide was used in actual industrial wastewater treatment. After 30 days of continuous operation, the adsorption performance showed no significant decline, the removal rate of heavy metal ions remained stable at over 95%, and the effluent quality met the national discharge standards. S8.

3. Simultaneously, the material is easily regenerated, and after 10 cycles of pickling and heat treatment, its structural integrity remains good, with the specific surface area maintained at 200 m². 2 With a yield of / g or more, it possesses the feasibility and economic advantages for large-scale industrial application.

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